Case study: Retrofitted heating system

A wastewater treatment plant heating system required conversion from generating low-pressure steam to heating hot water

By Ian Marchant and April Ricketts September 21, 2020

At an existing wastewater treatment facility, a fuel-oil-fired cast-iron steam boiler was originally designed to provide space heating to multiple process buildings using a sitewide utility tunnel system. As additional heating, ventilation and air conditioning systems were added to the heating loop, those systems were served by hot water generated by a steam-to-hot water converter and base mounted centrifugal pump system.

As part of a recent renovation project at the wastewater treatment plant, the existing heating system was converted from generating low-pressure steam to heating hot water, which required replacement of steam cast iron sections and controls with components suitable for a heating water system as well as removal of the steam to hot water converter, steam piping, unit heaters and accessories.

Once the boiler was converted, pressure testing the boiler and updating the nameplate were incorporated as per the local boiler code requirements. As part of the conversion process, a new natural gas burner along with two base-mounted centrifugal pumps were added and the existing gas flue replaced. Combustion air into the space was ducted from a new combustion air louver and included a supply fan and preheat coil to temper the combustion air before entering the existing mechanical room. Outside air temperature reset was included with the new boiler controls.

The boiler and related equipment are housed in a mechanical room located away from the corrosive chemical areas and piping. Hangers and accessories running through corrosive spaces were required to include protective coatings suitable for the unique environments.

Author Bio: Ian Marchant is a senior mechanical engineer at CDM Smith. He has more than 30 years of experience in the building system and energy fields. April Ricketts is a senior mechanical engineer at CDM Smith. She has 24 years of experience in the design of building mechanical and plumbing systems.